fix a docker build dependency

Add Nomad Service Discovery Support

Adds 2 functions for retrieving services from Nomad:

- nomadServices - retrieves all services from Nomad
- nomadService - retrieves all registrations for a service

Tag filtering for `nomadService` is currently implemented in
consul-template as the Nomad API does not support it directly.

Tests use a Nomad binary on path and require Nomad 1.3.0-beta or a
binary built from the PR: hashicorp/nomad#12458

Tests also require Docker.

Version 0.28.1

Version 0.28.0

Version 0.27.2

Version 0.27.1

Version 0.27.0

Version 0.26.0

Version 0.25.2

Version 0.25.1